Filter circuitry using active inductor

Abstract

A filter circuitry () using an active inductor is disclosed. The filter circuitry () has a first terminal (In/Out) and a second terminal (In/Out). The filter circuitry () comprises a first transistor (M) and a second transistor (M). The filter circuitry () further comprises a first switch (S), a second switch (S), a first capacitor (C), a second capacitor (C) and a resistor (R). The first and second transistors (M/M) together with the resistor (R) and the first and second switches (S/S) are connected in a current mirror topology. The first and second capacitors (C/C) are connected at the first and second terminals of the filter circuitry () respectively. The filter circuitry () is configurable to either have the first terminal (In/Out) as input and the second terminal (In/Out) as output or have the first terminal (In/Out) as output and the second terminal (In/Out) as input by changing on-off states of the first and second switches. The transistors are interconnected in a current-mirror fashion. Depending on the switch position one of the transistors also acts as part of an active inductor such that the circuit functions as a low pass filter with a complex pole pair and a real pole. Depending on the switch position the LPF allows signal flow in either direction. For use in a TDD environment in combination with a passive mixer ().